This invention relates to cement slurry reclamation techniques for ready-mix concrete plants in which the aggregate and coarse sand constituents are separated from returned concrete mix and the remaining ingredients are stored in slurry form for total consumption during the following production day.
U.S. Pat. No. 4,226,542 issued Oct. 7, 1980, for "Cement Slurry Reclamation System and Method", the disclosure of which is hereby incorporated by reference, illustrates a slurry reclamation system for use with a concrete ready-mix plant which enables one hundred percent reclamation of the constituents of concrete mix returned to the plant site by vehicles. Returned concrete mix is dumped into an inlet hopper having a screw classifier for removing aggregate and coarse sand, and a weired channel enabling gravity flow of the water, cement fines and sand fines constituents into a slurry vessel. The slurry vessel is sized in such a manner as to guarantee complete consumption of the slurry returned during a day's production by the end of the following production day, the volumetric capacity of the vessel being related to the total average volume of water used to produce fresh concrete during a representative production day.
The slurry is consumed by admixture to fresh water, cement, sand and aggregate at a rate selected in accordance with the slurry specific gravity and the scheduled or estimated production requirements for that particular day. As disclosed more fully in the above-referenced patent, the percentage of slurry to be admixed to the fresh ingredients is selected by the operator and determined by the slurry vessel working level volume, the measured specific gravity of the slurry (typically obtained at the beginning of the production day) and the scheduled day's production. Typically, the operator manually selects a programmed amount of cement, sand, aggregate and water by weight into a set point controller physically incorporated in the batching console in the ready-mix plant, the amounts being determined by the operator in accordance with the concrete design mix figures normally used by the operator. Next, the set point amounts of these ingredients are then modified or compensated for in accordance with the percentage of slurry activity (a predetermined figure), the specific gravity obtained from a density cell and the percentage of slurry substitution obtained from the day's production schedule. It should be noted that the set amount of the aggregate by weight is normally unaffected by the slurry values, since the slurry ordinarily contains no aggregates. The batch controls for cement, water, sand and aggregate are then used to meter the relative amounts of the constituent ingredients from the water supply and the storage bins for the dry ingredients to the ready-mix mechanism.